c# - WebClient DownloadDataAsync 当前下载速度

Question

我正在尝试获取 WebClient 下载文件的当前下载速度，但是当我使用一个我确信应该可以计算出的公式时:

Stopwatch.Stop();
double msElapsed = Stopwatch.Elapsed.TotalMilliseconds;
int bytesDownloaded = (int)e.BytesReceived - lastBytesDownloaded;
double downloadSpeed = (double)bytesDownloaded / (msElapsed / 1000);
lastBytesDownloaded = (int)e.BytesReceived;
Stopwatch.Restart();

其中 Stopwatch 是我在开始文件下载时启动的秒表，lastBytesDownloaded 是一个类变量，这一切都在 downloadProgressChanged 事件内，但是下载速度与实际速度相差很大。

例如，如果我以 500kb/s 的速度下载文件，它会完全随机地从(例如)10kb/s 快速跳跃到 50mb/s。

通过对其进行一些编辑，我可以获得准确的平均下载时间:

double sElapsed = Stopwatch.Elapsed.TotalSeconds;
int bytesDownloaded = (int)e.BytesReceived;
double downloadSpeed = bytesDownloaded / sElapsed;

但这不是我想要的。如何获得更稳定的当前下载速度读数？

Answer 1

您只需要smooth较长一段时间内的数据。例如，不要仅根据最后一次测量来报告当前下载速度；使用(也许weighted)moving average相反。

简单的例子:

var measurements = 0, maxDataPoints = 5;
var dataPoints = new double[maxDataPoints];

然后:

Stopwatch.Stop();
double msElapsed = Stopwatch.Elapsed.TotalMilliseconds;
int bytesDownloaded = (int)e.BytesReceived - lastBytesDownloaded;
lastBytesDownloaded = (int)e.BytesReceived;
double dataPoint = (double)bytesDownloaded / (msElapsed / 1000);
dataPoints[measurements++ % maxDataPoints] = dataPoint;

double downloadSpeed = dataPoints.Average();
Stopwatch.Restart();